Saturday, June 19, 2010

Why does a living organism have different types of cells?

Your body is made of about 10 trillion cells. The largest human cells are about the diameter of a human hair, but most human cells are smaller -- perhaps one-tenth of the diameter of a human hair.

Run your fingers through your hair now and look at a single strand. It is not very thick -- maybe 100 microns in diameter (a micron is a millionth of a meter, so 100 microns is a tenth of a millimeter). A typical human cell might be one-tenth of the diameter of your hair (10 microns). Look down at your little toe -- it might represent 2 or 3 billion cells or so, depending on how big you are. Imagine a whole house filled with baby peas. If the house is your little toe, the peas are the cells. That's a lot of cells!

At a microscopic level, we are all composed of cells. Look in a mirror -- what you see is about 10 trillion cells divided into about 200 different types of cells. Our muscles are made of muscle cells, our livers of liver cells, and there are even very specialized types of cells that make the enamel for our teeth or the clear lenses in our eyes!

If you want to understand how your body works, you need to understand cells. Everything from reproduction to infections to repairing a broken bone happens down at the cellular level. If you want to understand new frontiers like biotechnology and genetic engineering, you need to understand cells as well.

Quick Review

All life is made of cells.

Most scientists divide life into 5 separate kingdoms (Plants, Animals, Protists, Moneran, %26amp; Fungi) based on their similarities and differences.

Some life forms are very simple and made of only one cell (Moneran, Protists, some Fungi).

Other life forms (Animals, Plants, some Fungi) are made of many cells that work together

In the last lesson we saw what most cells have in common. When you hear the word cells or study cells you can put a picture in your mind of what a cell looks like. You are familiar with the basic parts of all cells, like a cell membrane, the nucleus, and the mitochondria.

In this lesson, our purpose is to see how cells are different. We call this cell differentiation. In the nucleus of each cell you will find small structures called chromosomes. These hold the plan, like a set of blueprints, which decides what a cell will look like and what its job will be.

A maple tree is an example of a complex organism. It has many cells, but some of the tons of cells do one job, while some of the tons of cells do another job. That is why if I handed you a piece of a maple tree you could tell right away if it was a piece of bark, root, or a leaf.

Each of those parts are made of cells. Each type of cell (leaf cells, bark cells, etc.) has a special task to do so the tree can survive. The leaf gathers sunlight to make food for the tree, but obviously the roots, being underground, away from the sun, don鈥檛 do the same job. They bring water to the leaves and anchor the tree in place. A leaf cell can only make more leaf cells and a bark cell can only make more bark cells.

All types of complex organisms have different cells to do different jobs. To better understand cell differentiation we are going use an example with which you are very familiar --- your body.

FUN FACT: All cells are 90% water.

How are Cells organized?

Every living thing is made of separate cells. They can do their specific job, and work together.

Cells in your body are organized like a school district is organized. In a school there are levels of organization. Students are organized into classes. Classes are organized into grade levels. Grade levels are organized into schools. Schools are organized into a school district.

Life forms have a similar arrangement. Individual cells join together to form tissue, like muscle tissue, bone tissue, or skin tissue. Tissues join together to form organs, like your lungs, your brain, or your intestines. Organs join together to form a whole body system, like the skeletal system, nervous system, or the digestive system. All the body systems join to form the organism.

Comparing cells to schools would look something like this:

Example in a person

Level of organization in a person

Level of organization in a school

Muscle cell



Muscle tissues



Heart muscle


Grade Levels

Circulatory System

Organ Systems




School District

Let鈥檚 Get Moving!

What happens when you run, jump, swim, just tap you fingers on the desk, or even yawn? Muscles help your body do these actions. Plants don鈥檛 move around so they don鈥檛 need muscle tissue which is made of muscle cells. These long stringy fibers can pull together and then relax. When a muscle cell in your body contracts, it is using energy to move some part of you. You know muscle cells in your arms are working when you pick up a heavy box. But they鈥檙e even busy extending and contracting when you smile, frown, breathe, or laugh.

Your heart muscle cells NEVER get a break, keeping your heart beating even when you are asleep.


Plants have a layer of outer cells to protect what鈥檚 inside, just like that plastic sandwich bag protects your bologna and cheese sandwich. You have a protective layer, too --- your skin cells. Touch your hand and you鈥檙e touching many thousands of skin cells. All of your outer cells (the ones you can touch) are dead. But just underneath this surface are neat rows of living skin cells.

Squeezed in between those skin cells are other types of cells; nerve cells, which allow you to feel things; fat cells that keep you warm; and capillary cells that make sure all the cells are supplied with oxygen and nutrients from your bloodstream. Skin cells are shaped a little like building blocks, all fitting neatly together and holding all of you together.

The Eyes Have It

Your eyes have nerve cells that turn light into electrical impulses and then send them to your brain. Cone shaped cells pick up bright lights and colors and rod-shaped cells respond to dimmer signals. The retina of your eye contains about 137 million light-sensitive cells in an area about one square inch. There are 130 million rod shaped cells for black and white vision and 7 million cone cells for color vision. Dogs also have special light sensitive cells called cones, which are needed for color vision. However dogs don鈥檛 have as many cones, or as many types of cones, as people do. Dogs see greenish-blue colors as white or grey. They can tell the difference between blues and reds, but confuse colors ranging between greenish yellow and red. This means your dog may have a hard time spotting a red ball on a green lawn.

Bone Cells %26amp; Fat Cells

Bone cells aren鈥檛 all hard and brittle, like you might think. Like your other cells, they are soft and surrounded by membranes. But these cells need calcium and are grouped to form bony tissue. Without our bony skeleton to hold us up, we鈥檇 sink to the ground in a big heap.

Fat Cells look like a bunch of bubbles. They store energy and help insulate the body from cold. When you eat more calories than your body can use that day, your body stores that extra energy as fat, for later. If you run a long race or participate in a strenuous sporting event, you may need more energy than your body has taken in that day. You fat cells are ready to keep your body energized for those intense times.

Your body has many other types of cells. Each type has a specific job and looks different from other cell types, but does look like other cells of the same type. Bone cells look like other bone cells, but look nothing like liver cells.

Tools for Viewing Cells

A magnifying glass can magnify a cell 10-20 times.

An average microscope can magnify a cell 40, 100, %26amp; 400 times. An advanced optical microscope can magnify a cell 2,000 times.

An electron microscope can magnify a cell 1 million times.


Check out these helpful Web sites (current June 2004)

Heart Muscle Cell

Image copyright Dennis Kunkel.

Here is a micrograph (a photo taken through a microscope) of the muscle tissue in a human heart.

Why does a living organism have different types of cells?

The six characteristics of living things, and an explanation of each one.

Theme #1 - Cells

All living things are composed of one or more cells. Different types of cells have different "jobs" within the organism. Each life form begins from one cell, which then will split. These cells split, and so on. After this has happened several times, differentiation is undergone, when the cells change so that they are not the same thing anymore. Then they are used to begin to put together the final organism, some cells, for example, as the eyes, some as the heart, etc. The only arguable exception to this is viruses. They are not composed of cells, but are said to be "living."

Theme#2 - Organization

Complex organization patterns are found in all living organisms. They arrange themselves on very small levels, grouping like things together. On larger levels, they become visible. This also has to do with differentiation, as the cells are organized in a manner that makes sense for the organism after they change to what they鈥檒l be in the final organism.

Theme#3 - Energy Use

All organisms use energy. The sum of the chemical energy they use is called metabolism. This energy is used to carry out everything they do. Autotrophs (plants) use energy from the sun for photosynthesis, to make their own 鈥榝ood鈥?(glucose). Heterotrophs (animals and humans) must ingest food for this purpose.

Theme#4 - Homeostasis

All organisms have stable internal conditions which must be maintained in order to remain alive. These include temperature, water content, heartbeat, and other such things. In a way, this has to do with energy use, because a certain level of energy must be kept within the body at all times. For this, obviously, humans must then ingest food on a regular basis. Not all conditions are for the body to maintain itself; though most are.

Theme#5 - Growth

All organisms grow and change. Cells divide to form new, identical cells. Differentiation happens, as well, when cells mutate into other types of cells, making a more complex organism. Organisms growing, changing, and becoming more complex is called development. Single-celled organisms do grow as well, but they will only become slightly larger 鈥?this is nearly unmeasurable.

Theme#6 - Reproduction

All organisms reproduce in order to continue the species' life. This is combining genetic information (in sexual reproduction) or splitting into two organisms (in asexual reproduction) in order to create another of the same species. In sexual reproduction, the new organism will have some characteristics from the mother, and some from father. It may look like either of them, or it may not. In asexual reproduction, the new organism is an exact copy of the first. Sometimes, not every member of a species is able to reproduce. As long as others are (which we know they can, if they still exist today) then it does not threaten the species. (Except for mules, but don't worry about them, they are a bizarre anomoly.)

Why does a living organism have different types of cells?

Was that a question or an article ... in one sentence organisums have different types of cells to do different types of funttions... they r like cars ..different type of car for every purpose

Why does a living organism have different types of cells?

Wow, this is a question? Seems like a quick cut and paste to me. Yah like the first guy said different cells do different functions.

Why does a living organism have different types of cells?

because that is the way God made us. (and for other answerers this person wants to know why we have all thoes cells and things)

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